I would join a blogging network because of all the new opportunities and people I would meet. Being part of a community that helps one another grow is the best way for a startup blogger to gain exposure and knowledge, whereas if you are riding solo, you would have to experience everything the hard way: learning by trial and error. Trial and error can be time and finically consuming.
I will say however that blogging networks are only as good as the people you have in it. I say this because a blogging network is a community and if the community is made up of negative, trollish individuals that is the culture you will be joining.
The type of blogging network I see myself joining is a network of vloggers. A place where individuals mesh blogging and vlogging into one. Where not only can you read about what is going on but also watch what is going on. We would collaborate with one another to share new viewers and help each other gain exposure. Furthermore we would give one another tips on how to edit, or what was not appropriate before the content is sent out, sort of a rough draft phase.